The present invention relates to a method and a device for measuring the position of segments with one or more absorbing substances in multi-segment filter rods of the tobacco processing industry.
In order to make the filter effect of cigarette filters composed of cellulose acetate filters more effective and more selective, granulates of finely dispersed particles of absorbing material are often added to cellulose acetate filters. Active charcoal granulates are an example which due to a large inner pore surface absorb primarily unpolarized molecules from the tobacco smoke. Also included for this purpose, are other materials in powder form, such as finely dispersed tobacco, silica gel, or wood shavings that are incorporated into the cigarette filter. The granulate is introduced in a filter rod maker as a process step into the outspread cellulose acetate, before the arrival thereof for spraying of a plasticizer for forming the endless filter rod, which is then enclosed with paper and cut into individual rods. In a multi-segment filter rod maker, individual segments of differently doped filter rods are joined together, including pure cellulose acetate rods such that ultimately a finished filter element for a cigarette results from two or more segments.
Here, the concentration of the granulate is not uniformly distributed in the filter tow. The concentration depends both on the uniformity of the application as well as the uniformity of the subsequent compression of the filter tow into the filter rod during rod formation in the inlet funnel of the filter rod maker. The degree of compression depends on the ratio of the speed of the arriving, outspread filter tow to the speed of the endless filter rod. Consequently, it is of great interest to detect both the distribution of the granulate in the individual segments of the endless filter rod as well as the individual positions of the segment edges as a profile measurement, and to exclude imperfect filter rods from the production. A filter rod is imperfect then if the average value of granulate deviates too much from a predetermined target value, the distribution in the filter rod is too non-homogeneous, or the measured positions of the segment edges do not conform with the target values for the segment edges.
From the document DE 101 59 233 A1, the entire contents of which is incorporated herein by reference, a method is known for producing filters for filter cigarettes. With the method, a filter granulate is applied in cycles before the endless rod shaping device such that zones with granulate and without granulate, preferably of uniform length, alternate with each other in the endless filter rod. The transition from the zones without granulate to zones with granulate is detected using a microwave resonator. With the known method, both the shift of the resonance frequency and the spread of the resonance curve are detected and evaluated. Due to the volume expansion of the measurement region in the microwave resonator, the spatial resolution of the known method is too poor in order to detect the transition edge.